Indurated cellulosic product and method of making the same



Patented Jan. 1 7, 1933 UNITED STATES PATENT OFFICE DUNCALF W. HOLLINGWORTH AND LESTER W. TARR, OF NEWARK, DELAWARE, AS-

SIGNORS TO CONTINENTAL-DIAMOND FIBRE COMPANY, OF NEWARK, DELAWARE, A

CORPORATION OF DELAWARE INDURATEI) LELLULOSIC PRODUCT AND METHOD OF MAKING THE SAME No Drawing.

Our invention relates to a novel indurated cellulosic product and to the method of making it, and more particularly it relates to an indurated cellulosic product having the general properties of vulcanized fibre, but -su- I provide an indurated cellulosic product of novel and valuable characteristics in which a physical and chemical modification of the cellulose has taken place as is shown by the large decrease in cuprammonium viscosity of the finished product as compared to the cuprammonium viscosity of the original cellulosic sheets from which the product is made.

A further object of our invention is to furnish a cellulosic product having certain properties which are comparable to those of vulcanized fibre, such for example as hardness, specific gravity, and hygroscopicity but which at the same time has greater strength, toughness, and dielectric strength than vulcanized fibre.

Still another object of our invention is to provide an indurated product which not only has the properties hereinbefore mentioned but which because of its uniformity and texture may be machined easily and accurately and is capable of being highly polished. The product may also be subjected to various treatments under heat to form products of desired shape with assurance that the mateteral will set in whatever form is given it while under heat, and with the further assurance that thereafter it will not become appreciably brittle under-a reasonable application of heat.

Other objects of our invention, including the novel method of producing the indu- Application filed January 8, 1932. Serial No. 585,634.

rated product, will be apparent from a cons .deration of the specification and claims.

Heretofore, vulcanized fibre has been manufactured by treating paper sheets with sulphuric acid or zincchloride, or more occasionally with phosphoric acid. The use of a mitxure of these chemicals has also been suggested but in all these methods, the properties of the vulcanized fibre are confined with- 111 definite limits which has restricted the use of the product to a considerable extent. The product of the present invention is prepared by treating paper sheets under suitable conditions with a bath comprising phosphoric acid, sulphuric acid, and acetic acid. Any highly absorbent unsized paper may be employed such as cotton. paper or alpha cellulose paper, the latter being preferred in most instances. The treating bath should contain less than 25% of water by weight, and preferably should contain less than 15% of water by weight. It may be made up by employing orthophosphoric acid of a concentration from 85% to 96.6%, sulphuric acid of a concentration from 93% (sp. gr. 1.83) to fuming (100%H,So,+15%SO8),

and acetic acid of a concentration from 90% to glacial (99.6% sp. gr. 1.052). In the case of the acetic or the phosphoric acid, the anhydride may be employed if desired It is to be understood that these concentrations are merely illustrative and that the choice of the concentration of the particular acids used may be determined by the amount of water desired in the bath. The optimum water content of the bath} is in most instances, from 10% to 14% by weight. The proportion of the three acids employed may be varied widely but if employed in the ratio (by volume) of 100 parts of phosphoric acid to 5 to 25 parts of sulphuric acidto 5 to 30 parts of acetic acid, excellent results are obtained. A particularly desirable product is obtained employing 100 volume parts of phosphoric acid of 85% concentration, 20 volume parts of sulphuric acid of 93% concentration and 10 volume parts of glacial acetic acid, the Water content of the bath,

resulting from the use of acids of these concentrations, being 12.97% by weight.

The paper sheets which may or may not have been heated to remove some or all of the moisture are subjected to the chemical action of the bath which may be at a temperature somewhat above that of room temperature until the desired reaction of the cellulose with the medium which will permit satisfactory lamination has taken place. This reaction usually requires only a few seconds. The treated cellulose sheet is then laminated to the desired thickness according to standard practices employed in the manufacture of vulcanized fibre.

The laminated productis then allowed to set for a period of time in a humid atmosphere. This treatment is designated herein as the time-set, and the length of time of treatment depends on the other factors of the process including the amount of mois ture in the original paper sheets, the temperature of the bath, the relative humidity employed in the time-set, and the temperature used therein. If the moisture in the paper is 2% or 3% or less; if the temperature of the bath is less than F.; if the relative humidity of the time-set is less than 40% and greater than 20%; and if the temperature employed during the time-set is less than 70 F., a time-set of two hours will be found to give excellent results. If, for example, however, the moisture in the paper is from 4% to 8%, or the temperature of the bath is in the neighborhood of 85 F., or the relative humidity is appreciably above 40%, or the temperature during the time-set is appreciably above 70 F., then the length of time of the time-set may be decreased, for example, to fifteen minutes. After the laminated product has been sub.- jected to the time-set, it is washed and dried according to the well known method of processing vulcanized fibre.

The treatment of the paper by the chemical bath containing the three acids andthe subsequent time-set herein-described causesa physical and chemical modification of the cellulose. This chemical and physical modification is apparent not only in appearance and physical properties of the product itself but is also evidenced by the decrease in cuprammonium viscosity of the finished product as compared to that of the original paper from which the product is made. The cuprammonium viscosity of cellulose has become recognized in the art as a measure of the physical and chemical condition of the cellulose. In the tests employed herein, the cuprammonium solution of a concentration that eontains13.7 grams of copper per liter and 221.5 grams of ammonia (NH per liter is made by precipitating the copper hydroxide from an aqueous solution of copper weight at 105 C. In the case of the vulcanized fibre and the product of the present invention, the product is rasped with a file, passed through a twenty mesh sieve, and weighed and dried as in the case of paper.

The viscosity determinations are made with a special viscosimeter originally suggested by Glibbons and Geake of the Shirley Institute (J. Text. inst. vol. 19, p. 77, 1928). The cellulose solutions are prepared in the capillary viscosimeter which is completely filled with the solvent and the fibrous material. The tube is then stoppered and wrapped in black cloth or kraft paper to exclude both air and light. Adequatemixing of the solution is obtained-by means of a short steel rod which travels from one end of the tube to the other when it is fastened on a wheel rotating at the rate of four revolutions per minute. In the case of the present determinations, 1% cellulose solutions are used and after rotating on the wheel for twenty-four hours, the viscosity determinations are made in duplicate at 25 C. Tests show that with vulcanized fibre prepared by the usual treatment with zinc chloride, the percentage of reduction of viscosity of the vulcanized fibre from that of the original paper is low, increasing somewhat when higher temperatures of treatment are used. The percentage reduction in viscosity for the vulcanized fibre tubing ranges from 1.52% to 24.30%. In the product of the present invention, tests show that the percentage reduction of viscosity is high, always being above 40%, the greatest reduction occurring in products made from alpha cellulose. In eleven tests with products .made from alpha cellulose, the percentage reviscosity was 47.5%. Thus it will be evident that'the cellulosic sheets have undergone a marked degradation as compared to vulcanized fibre, since with the products of the present invention, the cuprammonium viscosity has been markedly reduced as compared to that of the original paper from which the products were made.

In a typical case, the bath for the chemical treatment is prepared as follows: 20 milliliters of sulphuric acid of 1.83 specific gravity are added to 100 milliliters of orthophosphoric acid of 85% concentration. The mixture is cooled to room temperature in order to lessen the loss by volatilization and 10 milliliters of glacial acetic acid of 1.052 specific three times, filtering,"

. made up as described weighs 219.9 grams and has a specific gravity of 1.691 at 69 F. The

. bath contains 28.51 grams of water or 21.92%

of water by volume or 12.97% of water by weight. The water content of the bath is 12.97%.

Alpha cellulose paper, unsized, of a thickness of .010 inches is heated above room temperature until it contains about 2% moisture and is passed through the preferred bath at such a speed as to bring the paper into contact with the solution for a few seconds. The excess solution is removed by scraper bars and the gelatinized paper is then laminated to the desired thickness according to standard practices employed in the manufacture of vulcanized fibre. For example, it may be wound on a brass or glass mandrel in the makin of tubes or it may be wound on a large cy inder and subsequently cut off to form sheets. Heat may be applied to the bath during the. treatment, if desired, but it has been found that a better .productis obtained if no heat is employed. In this respect, the process differs from that used in the manufacture of the ordinary vulcanized fibre where heat is always used.

The laminated product is allowed to set for a given period of time in a humid atmosphere at a given temperature. It has been I found that a set for two hours in a relative humidity of from 25% to 40% at 60 F. to 70 F. gives the best results. After sett'ng,

the product is washed and dried according viscosity of 4.98 centipo ses for a 1% solution at 25 C. determined in the same manner, or a reduction of 15.79 centipoises or a percentage reduction in viscosity of 76%.

The product which results from the above described procedure is hard, horny, tough, somewhat translucent and also somewhat thermoplastic both when dr a K d moist. It possesses some properties which are compara ble to ordinary vulcanized fibre, such for example as hardness, specific gravity and hygroscopicity. Its uniformity and texture are such that it can be machined eas ly and accurately. Its surface is capable of taking a high polish as by bufiing or other polishing processes.

In certain respects, the product possesses properties which are greatly superior to ordinary vulcanized fibre. It has in high degree the property of flowing under pressure as in a die, a property which is materially increased by the application of heat. The product differs from vulcanized fibre since it flows read-- ily in a dry condition under heat, while, in the case of vulcanized fibre, a moist product is required for successful forming, Extruded washers, for example, have been fabricated with a shank measuring .070" and a flange of only .023". Tubes may be expanded in diameter, or spun, or pressed in a heated die. a

In the case of sheets, strips .050" in th ckness may be safely rolled down to .028" in thickness. Such strips under heat. may be bent double without cracking. The material sets in whatever form it is molded and does not become brittle under a reasonable application of heat, nor does t warp appreciably after such setting. A moisture content of from 3% to 6% is conducive to flexibility under heat, although satisfactory results may be obtained with the material dry.

This new fibreproduct has a strength and a toughness far superior to vulcanized fibre. For example, in the manufacture of a certain type of tubing, a torque test is involved where a requirement of 20 foot ounces with a minimum of 16 foot ounces has to be met under certain prescribed conditions. On a d fferent size of tubing, under the same conditions, a torque of 35 foot ounces with a minimum of 30 foot ounces is required. Both of these requirements can just be met with tubing made by the usual vulcanized fibre process, but manufacturing vulcanized fibre to meet this test does not constitute a satisfactory commercial operation. With the fibre product of the present invention, an average torsional strength of 35 to 55 foot ounces respectively is obtained for the two types of tubing mentioned. Thus, it will be seen, that tub ng made in accordance with the present invention is meeting a requirement that ordinary vulcanized fibre and other known products are unable to meet.

Standard vulcanized fibre has a dielectric strength of '320 and 338 volts per mil respectively for the two types of tubing mentoned above, whereas the new product has a dielectric strength of 710 and 523 volts per mil respectively. The product of this lnvention,

thtrefore, possesses a dielectric strength superior to vulcanized fibre In a typical case employing gray cotton paper of .007 inches thickness, the paper is I passed through a bath composed of 100 milliliters of 85% orthophosphoric acid, 20 milliliters of 93% sulphuric acid, and 10 milliliters of glacial aceticacid, the water content of the bath being 12.97% by weight. The cotton paper contains 3.5% moisture and is brought into contact with the solution at a temperature of 70 F. for a few seconds. It is then treated and laminated in the same In all the alpha cellulose paper (unof .010 thickness was employed. In 70 all cases, it was predried at 105 C. to 1109 C. for fifteen to twenty minutes. The timeinstance was two inside 80 manner as that described for the treatment three acids, difi'erent amounts of water in of alpha cellulose paper and is thereafter the bath, various bathtemperatures, and varisubjected to a time-set of two hours inan ous humiditiesin the time-set. atmosphere of 30.7% relative humidity at tests in the table 70.5 F. Itis then washed and dried. A i d tube with an outside diameter of .420 inches and an inside diameter of .333 inches has a torsional strength of 41.3 foot ounces while em ed in each b of 7 Outslde dlameter. and hours. lhil torsional strength was deter- 10 .307 1351M; insf1dediameterTlllla ttorslonal mined in accordance with standard tests, and a O i f fi a i a the results are expressed in foot ounces, the 856 mm 10 e Pro 1S ma a columns A and B ivin the results of tests cuprammomumvlscoslty of cen-tlpolses of tubes of 111 outsi d dizmeter of 120 inches for a 1% solution at 25 C. determlned by e the method hereinbefore described. while the t Inches reipectlvely and 0 diameter of .333 inches and .307 inches rey. The viscosities were determined in the manner hereinbefore described and are for 1% solutions at 25 C. The original alpha cellulose paper before treatment had a viscos- 85 ity of 20.77 centipoises fora 1% solution at g difierent amounts of the 25 'C.

Viscosity Centipoises Torsional strength y and of an inside Rel. hum.

Torsional strength t1vel Room. temp. F. of timeset set 3 inches and .307 inches re- Table II represents the results 11 tubes made from gray cotton able III represents results obbes made from red cotton pa- Data Time

Data

Room Rel. hum. temp. of of time time set mammmwwmmmm .372 inches respec ameter of .33 ectively. tained wit Bath F. set min.

Bath

paper while T water by wgt. temp.

TABLE I ht temp. F.

3112042137 9100798981 3 7 0 1 .L2Z3i the tained with tu TABLE II 7 CHJCOOH %H;O m1. (99.6%) by weig 0 5 mwawwzaw CHaCOOH th in tubes made and the torsion- Composition of bath 93% rnso. ml.

Composition of bath H2804 ml.

of a thickness of .007 di lengths of time in the s her Variables as apthe results of tests per.

85 HzPO4 mmwwmmwwwmw In the tables, ressed in foot ounces, giving or Tables II and III show the of tubes of an outside diameter of .420 inches 1 %water in paper g various obtained by us Sample No.

The followin variation 1n torslonal stren from cotton paper 2: columns A and B Sample No.

inches usi'n time-set as well as 0t pears therefrom. a1 stren th 1s ex TABLE III Composition ol bath Data Torsional strength ter Room Sample No. 3 W8 paper 85% 93% 99. 6% W temp.

a water Bath Time Rel. hum. 55? 5 S Q by wgt. temp F. set min. A B

set

As hereinbefore pointed out, considerable modification is possible in the type of paper treated, in the ratio of the three acids to each other, andin the amount of water in the bath as well as in the steps employed in processing the'paper including the temperature of the bath and the factorsinvolved in the timeset, without departing from the essential features of our invention.

l/Ve claim:

1. A tough, indurated product of physically and chemically modified cellulose, being thermoplastic under heat when dry and having a viscosity in cuprammonium solution of more than 40% less than the cuprammonium viscosity of the original cellulose. 2. A tough, indurated product of physically and chemically modified cellulose, being thermoplastic under heat when dry and having a viscosity in cuprammonium solution of more than less than the cuprammonium viscosity of the original cellulose.

3. A tough, indurated product of physically and chemically modified alpha cellulose, being thermoplastic u or heat when dry and having a viscosity in cuprammonium solution of more than 40% less than the cuprammonium viscosity of the original alpha cellulose.

4. A tough, indurated product of physical ly and chemically modified alpha cellulose, being thermoplastic'under heat when dry and having a viscosity in cuprammonium solution of more than 60% less than the euprammonium viscosity of the original alpha cellulosic base.

5. A tough, indurated product of physically and chemically modified cotton paper, be-

ing thermoplastic under heat when dry and having a viscosity in cuprammonium solution of more than 40% less than the cuprammonium viscosity of the original cotton paper.'

6. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid and acetic acid.

7. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent alpha cellulose paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid and acetic acid.

8. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 25% water by weight.

9. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid andcontaining less than 15% water by weight.

10. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent alpha cellulose paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid,-and acetic acid and containing less than 15% water by weight.

11. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 15% water by weight, the three acids being present in the bath in the ratio of 100 volume parts of phosphoric acid. to 5 to 25 volume parts of sulphuric acid to 5 to 30 volume parts of acetic acid.

12. The process of making an indurated product of physically and chemically modi- .fied cellulose which comprises subjecting an absorbent alpha cellulose paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 15% water by weight, the three acids being present in the bath in the ratio of 100 volume parts of phosphoric acid to to 25 volume parts of sulphuric acid to 5 to 30 volume parts of acetic acid.

13. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 15% water by weight, the three acids being present in the bath substantially in the ratio of 100 volume parts of phosphoric acid to 20 volume parts of sulphuric acid to volume parts of acetic acid.

'14. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 25% water by weight, laminating the treated sheet to obtain the thickness desired, and thereafter subjecting the laminated product to a time-set in a humid atmosphere.

15. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than water by weight, laminating the treated sheet to obtain the thickness desired, and

thereafter subjecting the laminated product to a time-set in a humid atmosphere.

16. The process of making an induratet product of physically and chemically modified cellulose which comprises subjecting an absorbent alpha cellulose paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and contaim ing less than 15% water by weight, laminating the treated sheet to obtain the thickness desired, and thereafter subjecting the laminated product to a time-set in a humid atmosphere. I I

17. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 15% water by weight, laminating the treated M sheet to obtain the thickness desired, and

thereafter subjecting the laminated product to a time-set for a period of from fifteen minutes to two hours in an atmosphere of greater than relative humidity at a temperature between 60 F. and 85 F.

18. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent alpha cellulose paper sheet to the action of a bath comprising phosphoric acid,

sulphuric acid, and acetic acid and containing less than 15% water by weight, laminating the treated sheet to obtain the thickness desired, and thereafter subjecting the laminating' product to a time-set for a period of from fifteen minutes to two hours in an atmosphere of greater than 20% relative humidiIty at a temperature between 60 F. and 85 i 19.-The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet to the action of a bath at a temperature in the neighborhood of 60 F. to 70 F. comprising phosphoric acid,

sulphuric acid, and acetic acid and containing less than 15% water by weight, the three acids being present in the bath in the ratio of 100 volume parts of phosphoric acidto 5 to volume parts of sulphuric acid to 5 to volume parts of acetic acid, laminating the treated sheet to obtain the thickness desired, and thereafter subjecting the laminated product to a time-set for a period in the neighborhood of two hours in an atmosphere in the neighborhood of 40% relative humidity and at atemperature less than 7 0 F.

20. The process of making an indurated product of physically and chemically modified cellulose which comprises subjecting an absorbent paper sheet containing less than 3% water to the action of a bath in theneighborhood of F. to F. comprising phosphoric acid, sulphuric acid, and acetic acid and containing less than 15% water by weight, the three acids being present in the bath in substantially the ratio of 100 volume parts of phosphoric acid to 20 volume parts of sulphuric acid to 10 volume arts of acetic acid, laminating the treated s eet to obtain the thickness desired, and thereafter subjecting the laminated product to a time-set for a period in the-neighborhood of two hours in an atmosphere in the neighborhood of 40% relative humidity and at a temperature less than 7 0 F.

DUNCALF W. HOLLINGWORTH.

LESTER W. TAKE. 

